For now, Hertz is the twice-jilted suitor, while Avis Budget lies in wait, hamstrung by an extended regulatory review.

Travelers, though, are more likely to find suspense in a summer page-turner than this long-running courtship. “The reality is, if you ask most business travelers who owns what, they wouldn’t have a clue,” said Neil F. Abrams, a longtime car industry executive and consultant. “All they care about is continuity of the overall value proposition, meaning price and quality of service, and dependability of the brand they have an affinity for.”

Still, frequent travelers said they were concerned that with fewer players, car rental prices would go up.

Last week, the board of Dollar Thrifty recommended that shareholders take no action on Hertz’s latest proposal, valued at $72 a share, or $2.24 billion. “Hertz’s current offer does not represent a fair split of the economic value created by the combination of Dollar Thrifty Automotive Group,” Scott L. Thompson, its chief executive, said in a statement.

The Hertz exchange offer for Dollar Thrifty shares, made on May 9, topped a bid from Avis Budget in September, now valued at $1.8 billion. The bidding first started in April 2010.

Dollar Thrifty, whose stock is trading around $80, up from 62 cents in March 2009, is in a position to be coy, analysts say. Some suggest the company could fetch up to $100 a share. In the meantime, Mr. Thompson said, “We will be monitoring the antitrust regulatory process and other circumstances carefully.”

A spokesman for the Federal Trade Commission, which reviews mergers and acquisitions, and challenges those that would probably lead to higher prices and fewer choices for consumers, said the commission did not comment on pending investigations.

A spokesman for Avis Budget declined to comment.

Richard D. Broome, a spokesman for Hertz, said, “We of course want to purchase the Dollar Thrifty Group at a fair price,” adding, “But at the same time, we have many significant ongoing initiatives to grow the business and provide even better customer service.”

No matter how the industry reshuffles, making a car rental reservation is no longer an afterthought, with rising gasoline prices, rental fees and taxes. The process takes much more planning than it used to. What is more, there will be more business travelers on the road this summer.

In its latest monthly review of reservations at big hotel chains in the top 25 markets in the country, the travel and hospitality company TravelClick found that summer business travel demand was up 7 percent from last year, based on reservations on the books. The business travel segment reflects travelers paying negotiated and nondiscounted retail rates.

“What we are seeing is a steady growth in business demand,” said Tim Hart, executive vice president of business intelligence at TravelClick. “As businesses travelers travel,” Mr. Hart added, “some portion are going to be renting cars.”

Don Metzger, president of Aniden Interactive, a digital design agency, said he, for one, would be doing so. “Being out there and staying in front of clients and customers is probably more crucial today than it ever has been,” he said.

Mr. Metzger said he had no allegiance to any one rental company, but he preferred four — Thrifty, Dollar, Avis and Enterprise — out of the 15 or so offered on sites like Travelocity. When he reserves a car, he said, he hews to the philosophy of acting as if he were spending his own money.

Recently, Mr. Metzger said he started using AutoSlash.com for business and leisure trips to find the lowest possible rate for a car rental. On a vacation trip to Maui, he said he saved nearly half on the price of an 11-day rental: He booked for $500 and the rate was ultimately reduced to $273. “If you can be judicious,” Mr. Metzger said, “it makes sense.”

Jonathan Weinberg, founder of AutoSlash.com, which constantly looks for lower rates for its customers, said he had been watching the moves for Dollar Thrifty carefully. Some markets, like Los Angeles or Orlando, are more competitive than others, like the New York metro area, where there are fewer companies to choose from, he said. “In the last year or so, people have been having sticker shock because of the price of a rental car,” Mr. Weinberg said.

In the universe of rental car companies, there is variation in pricing based on brands and their target customers, according to Mr. Abrams, whose consulting firm maintains a weekly pricing index that aggregates rates from the major car rental brands at 10 big airports.

A traveler who booked a midsize car at those airports for use on June 13, a week in advance, for example, would have paid $85.61 at Hertz, $80.39 at Avis, $86.78 at National, $63.10 at Budget and $57.39 at Dollar, according to the Abrams index.

A traveler who reserved a compact car for a week would have paid $299.37 at Hertz, $286.49 at Avis, $296.81 at National, $226.56 at Budget and $212.81 at Dollar, the index found. The prices exclude taxes, fees and surcharges, which can add 25 percent or more to the base rate in some markets.

Any consolidation at the top would not change those variations significantly, Mr. Abrams said. Over 30 years, with many ownership changes, the competitive price positioning of the brands has not changed much.

So which suitor for Dollar Thrifty will come out ahead? From a business and regulatory standpoint, Mr. Abrams said, Hertz had the advantage because it was not directly competing for Dollar Thrifty customers.

Avis Budget does compete with Dollar Thrifty, so has a tougher hill to climb for regulatory approval, he said.

Chris Brown, executive editor of Bobit Business Media, publisher of Auto Rental News, said Dollar Thrifty was attractive to Hertz and Avis Budget, two publicly traded companies, as they sought to control costs to compete against the privately held Enterprise Holdings.

Based on a 2010 market data ranking, Enterprise, made up of Alamo, Enterprise and National, was the dominant car rental company based on fleet, locations and revenue. Hertz, Avis Budget and Dollar Thrifty follow. A combination of Hertz and Dollar Thrifty or Avis Budget and Dollar Thrifty would close the gap with Enterprise, Mr. Brown said.

That eventuality is far from certain, though. “I do think that some deal will actually get made,” Mr. Brown said, adding, “But I certainly don’t have a clue on how, and I think most people in the industry don’t either.”

A version of this article appears in print on June 14, 2011, on page B6 of the New York edition with the headline: The Courtship of Dollar Thrifty. Order Reprints|Today's Paper|Subscribe